Tonic water is a carbonated soft drink that contains quinine, a natural alkaloid extracted from the bark of the cinchona tree. Quinine gives tonic water its distinctive bitter taste. Originally, tonic water was developed as a medicinal drink to prevent malaria, with much higher quinine content than modern versions. Today, tonic water typically contains much lower amounts of quinine and is sweetened to balance the bitterness, often with sugar or high fructose corn syrup

. Historically, quinine was used by the British in colonial India as a prophylactic against malaria, mixed with soda and sugar to make it more palatable. This led to the creation of the popular cocktail gin and tonic

. Modern tonic water is primarily consumed for its unique bitter flavor and as a mixer in various cocktails such as gin and tonic, tequila tonic, and vodka tonic

. Tonic water differs from other carbonated waters like club soda and seltzer in that it contains quinine and sweeteners, giving it a bittersweet taste, whereas club soda has minerals and a mildly salty flavor, and seltzer is plain carbonated water without additives

. In summary, tonic water is:

• A carbonated beverage flavored with quinine, giving it a bitter taste
• Originally used medicinally against malaria, now consumed mainly for flavor and as a mixer
• Sweetened to offset bitterness, containing sugar or other sweeteners
• A key ingredient in cocktails like gin and tonic